This example writes goal position of the Dynamixel and repeats read present position until it stops moving. The funtions that are related with the Read and the Write handle the number of items which are near each other in the Dynamixel control table, such as the goal position and the goal velocity.

Dynamixel series have their own control tables: Addresses and Byte Length in each items. To control one of the items, its address (and length if necessary) is required. Find your requirements in http://support.robotis.com/.

// Protocol version
#define PROTOCOL_VERSION 1.0 // See which protocol version is used in the Dynamixel

Dynamixel uses either or both protocols: Protocol 1.0 and Protocol 2.0. Choose one of the Protocol which is appropriate in the Dynamixel.

Here we set some variables to let you freely change them and use them to run the example code.

As the document already said in previous chapter, customize Dynamixel control table items, such as DXL_ID number, communication BAUDRATE, and the DEVICENAME, on your own terms of needs. In particular, BAUDRATE and DEVICENAME have systematical dependencies on your controller, so make clear what kind of communication method you will use.

Dynamixel basically needs the TORQUE_ENABLE to be rotating or give you its internal information. On the other hand, it doesn’t need torque enabled if you get your goal, so finally do TORQUE_DISABLE to prepare to the next sequence.

Since the Dynamixel has its own rotation range, it may shows malfunction if your request on your dynamixel is out of range. For example, Dynamixel MX-28 and Dynamixel PRO 54-200 has its rotatable range as 0 ~ 4028 and -250950 ~ 250950, each.

DXL_MOVING_STATUS_THRESHOLD acts as a criteria for verifying its rotation stopped.

These functions accept the key inputs in terms of example action. The example codes mainly apply the function getch() rather than the function kbhit() to get information which key has been pressed.

intmain(){// Initialize PortHandler instance
// Set the port path
// Get methods and members of PortHandlerLinux or PortHandlerWindows
dynamixel::PortHandler*portHandler=dynamixel::PortHandler::getPortHandler(DEVICENAME);// Initialize PacketHandler instance
// Set the protocol version
// Get methods and members of Protocol1PacketHandler or Protocol2PacketHandler
dynamixel::PacketHandler*packetHandler=dynamixel::PacketHandler::getPacketHandler(PROTOCOL_VERSION);intindex=0;intdxl_comm_result=COMM_TX_FAIL;// Communication result
intdxl_goal_position[2]={DXL_MINIMUM_POSITION_VALUE,DXL_MAXIMUM_POSITION_VALUE};// Goal position
uint8_tdxl_error=0;// Dynamixel error
uint16_tdxl_present_position=0;// Present position
// Open port
if(portHandler->openPort()){printf("Succeeded to open the port!\n");}else{printf("Failed to open the port!\n");printf("Press any key to terminate...\n");getch();return0;}// Set port baudrate
if(portHandler->setBaudRate(BAUDRATE)){printf("Succeeded to change the baudrate!\n");}else{printf("Failed to change the baudrate!\n");printf("Press any key to terminate...\n");getch();return0;}// Enable DXL Torque
dxl_comm_result=packetHandler->write1ByteTxRx(portHandler,DXL_ID,ADDR_MX_TORQUE_ENABLE,TORQUE_ENABLE,&dxl_error);if(dxl_comm_result!=COMM_SUCCESS){packetHandler->printTxRxResult(dxl_comm_result);}elseif(dxl_error!=0){packetHandler->printRxPacketError(dxl_error);}else{printf("Dynamixel has been successfully connected \n");}while(1){printf("Press any key to continue! (or press ESC to quit!)\n");if(getch()==ESC_ASCII_VALUE)break;// Write goal position
dxl_comm_result=packetHandler->write2ByteTxRx(portHandler,DXL_ID,ADDR_MX_GOAL_POSITION,dxl_goal_position[index],&dxl_error);if(dxl_comm_result!=COMM_SUCCESS){packetHandler->printTxRxResult(dxl_comm_result);}elseif(dxl_error!=0){packetHandler->printRxPacketError(dxl_error);}do{// Read present position
dxl_comm_result=packetHandler->read2ByteTxRx(portHandler,DXL_ID,ADDR_MX_PRESENT_POSITION,&dxl_present_position,&dxl_error);if(dxl_comm_result!=COMM_SUCCESS){packetHandler->printTxRxResult(dxl_comm_result);}elseif(dxl_error!=0){packetHandler->printRxPacketError(dxl_error);}printf("[ID:%03d] GoalPos:%03d PresPos:%03d\n",DXL_ID,dxl_goal_position[index],dxl_present_position);}while((abs(dxl_goal_position[index]-dxl_present_position)>DXL_MOVING_STATUS_THRESHOLD));// Change goal position
if(index==0){index=1;}else{index=0;}}// Disable Dynamixel Torque
dxl_comm_result=packetHandler->write1ByteTxRx(portHandler,DXL_ID,ADDR_MX_TORQUE_ENABLE,TORQUE_DISABLE,&dxl_error);if(dxl_comm_result!=COMM_SUCCESS){packetHandler->printTxRxResult(dxl_comm_result);}elseif(dxl_error!=0){packetHandler->printRxPacketError(dxl_error);}// Close port
portHandler->closePort();return0;}

// Initialize PortHandler instance
// Set the port path
// Get methods and members of PortHandlerLinux or PortHandlerWindows
dynamixel::PortHandler*portHandler=dynamixel::PortHandler::getPortHandler(DEVICENAME);

// Initialize PacketHandler instance
// Set the protocol version
// Get methods and members of Protocol1PacketHandler or Protocol2PacketHandler
dynamixel::PacketHandler*packetHandler=dynamixel::PacketHandler::getPacketHandler(PROTOCOL_VERSION);

getPacketHandler() function sets the methods for packet construction by choosing the PROTOCOL_VERSION.

index variable points the direction to where the Dynamixel should be rotated.

dxl_comm_result indicates which error has been occurred during packet communication.

dxl_goal_position stores goal points of Dynamixel rotation.

dxl_error shows the internal error in Dynamixel.

dxl_present_position views where now it points out.

// Open port
if(portHandler->openPort()){printf("Succeeded to open the port!\n");}else{printf("Failed to open the port!\n");printf("Press any key to terminate...\n");getch();return0;}

First, controller opens the port to do serial communication with the Dynamixel. If it fails to open the port, the example will be terminated.

// Set port baudrate
if(portHandler->setBaudRate(BAUDRATE)){printf("Succeeded to change the baudrate!\n");}else{printf("Failed to change the baudrate!\n");printf("Press any key to terminate...\n");getch();return0;}

Secondly, the controller sets the communication BAUDRATE at the port opened previously.

As mentioned in the document, above code enables Dynamixel torque to set its status as being ready to move.

dynamixel::PacketHandler::write1ByteTxRx() function orders to the #DXL_ID Dynamixel through the port which the portHandler handles, writing 1 byte of TORQUE_ENABLE value to ADDR_MX_TORQUE_ENABLE address. Then, it receives the dxl_error. The function returns 0 if no communication error has been occurred.

During while() loop, the controller writes and reads the Dynamixel position through packet transmission/reception(Tx/Rx).

To continue its rotation, press any key except ESC.

dynamixel::PacketHandler::write2ByteTxRx() function orders to the #DXL_ID Dynamixel through the port which the portHandler handles, writing 2 bytes of dxl_goal_position[index] value to ADDR_MX_GOAL_POSITION address. Then, it receives the dxl_error. The function returns 0 if no communication error has been occurred.

dynamixel::PacketHandler::read2ByteTxRx() functions orders to the #DXL_ID Dynamixel through the port which the portHandler handles, requesting 2 bytes of value of ADDR_MX_PRESENT_POSITION address. Then, it receives dxl_present_position and dxl_error. The function returns 0 if no communication error has been occurred.

Reading its present position will be ended when absolute value of (dxl_goal_position[index] - dxl_present_position) becomes smaller then DXL_MOVING_STATUS_THRESHOLD.

At last, it changes its direction to the counter-wise and waits for extra key input.

dynamixel::PacketHandler::write1ByteTxRx() function orders to the #DXL_ID Dynamixel through the port which the portHandler handles, writing 1 byte of TORQUE_DISABLE value to ADDR_MX_TORQUE_ENABLE address. Then, it receives the dxl_error. The function returns 0 if no communication error has been occurred.